1. Field of the Invention
The present invention relates to a winding jig, a method of manufacturing a polygonal coil using the winding jig, and a polygonal coil.
Priority is claimed on Japanese Patent Application No. 2007-63619 filed on Mar. 13, 2007, and on Japanese Patent Application No. 2008-43473 filed on Feb. 25, 2008, the contents of which are incorporated herein by reference.
2. Description of Related Art
Devices (cordless devices) having no cord and having a battery built therein, such as a mobile phone, an electric shaver, a desk cleaner, and a remote controller, have become wide spread. When a device having a secondary coil built therein is set to a charger having a primary coil built therein, electric power can be supplied from the charger to the device by means of electromagnetic induction between the primary coil and the secondary coil without providing a contact point where the charger and the device are connected to each other (see Japanese Patent Application, Publication No. 2005-136342 and Japanese Patent Application, Publication No. 2005-137173).
The secondary coil built in such a non-contact charging device needs to be thin. Accordingly, a coil (hereinafter, also abbreviated as a “one-line multi-layer winding coil”), which is obtained by winding in a diameter direction on a core in a one-line overlapping manner a conductive wire including a plurality of thin metal wires tied in a bundle, is used.
In the non-contact charger, a magnetic shielding sheet is usually attached to the secondary coil so as to protect electric circuit components from electromagnetic waves resulting from electromagnetic induction. When the secondary coil has a ring shape, no coil is disposed at four corners of the magnetic shielding sheet and thus eddy current occurs in the portions as shown in FIG. 12, thereby causing an increase in temperature. Accordingly, a polygonal coil as shown in FIG. 10 is necessary as the secondary coil.
However, it was conventionally difficult to make coils such as a one-line multi-layer winding coil, which is wound in the diameter direction on a core in an overlapping manner, have a polygonal shape with high precision.
For example, as shown in FIG. 11A, even when a conductive wire 6 is wound on a core 92 having a quadrangular prism shape in an overlapping manner by the use of a winding jig 9 in which the core 92 protrudes from the substantial center of a collar portion 91, the obtained one-line multi-layer winding coil 90 is not a shape to be called a polygonal coil but a shape close to a ring shape. Specifically, such a tendency is remarkable when the diameter of the core 92 is smaller than the outer diameter of the coil.
Therefore, in the past, as shown in FIG. 11B, a rectangular coil was shaped by pressing the outer peripheral portion of a ring-shaped coil from four sides indicated by arrows regardless of the shape of the core. By changing the pressing directions, other desired polygonal coils were obtained.
However, the coils obtained by such a press shaping method do not form precise polygons and do not satisfy characteristics of a secondary coil sufficiently.
As a result, there is no method of manufacturing a coil having a polygonal shape with high precision. Here, “a polygonal shape with high precision” means that the ratio of the curved portion to the outer peripheral edge portion of the polygonal coil is small.
The present invention is contrived to solve the above-mentioned problem. An advantage of the present invention is to provide a winding jig for manufacturing a polygonal coil with high precision, a method of manufacturing a polygonal coil using the winding jig, and a polygonal coil manufactured using the winding jig.